Wireless communication systems are evolving to meet the needs of providing continuous and faster access to a data network. In order to meet these needs, wireless communication systems may use multiple carriers for the transmission of data. A wireless communication system that uses multiple carriers for the transmission of data may be referred to as a multi-carrier system. The use of multiple carriers is expanding in both cellular and non-cellular wireless systems.
A multi-carrier system may increase the bandwidth available in a wireless communication system according to a multiple of how many carriers are made available. For example, a dual carrier system may double the bandwidth when compared to a single carrier system, a tri-carrier system may triple the bandwidth when compared to a single carrier system, etc.
In addition to this throughput gain, diversity and joint scheduling gains may also be expected. This may result in the improvement of the quality of service (QoS) for end users. Further, the use of multiple carriers may be used in combination with multiple-input multiple-output (MIMO).
By way of example, in the context of third generation partnership project (3GPP) systems, a new feature called dual cell high speed downlink packet access (DC-HSDPA) has been introduced in Release 8 of the 3GPP specifications. With DC-HSDPA, a base station (which may also be referred to as a Node-B, an access point, site controller, etc. in other variations, or types, of communications networks) communicates to a wireless transmit/receive unit (WTRU) over two downlink carriers simultaneously. This not only doubles the bandwidth and the peak data rate available to WTRUs, but also has a potential to increase the network efficiency by means of fast scheduling and fast channel feedback over two carriers.
For DC-HSDPA operation, each WTRU is assigned two downlink carriers: an anchor carrier and a supplementary carrier. The anchor carrier carries all physical layer dedicated and shared control channels associated with transport channels, for example, the high speed downlink shared channel (HS-DSCH), the enhanced dedicated channel (E-DCH), and the dedicated channel (DCH) operations. Such physical layer channels include, by way of example, the fractional dedicated physical channel (F-DPCH), the E-DCH HARQ indicator channel (E-HICH), the E-DCH relative grant channel (E-RGCH), the E-DCH absolute grant channel (E-AGCH), the common pilot channel (CPICH), the high speed shared control channel (HS-SCCH), and the high speed physical downlink shared channel (HS-PDSCH), and the like). The supplementary carrier may carry a CPICH, an HS-SCCH and an HS-PDSCH for the WTRU. The uplink transmission remains on a single carrier in current systems. The high speed dedicated physical control channel (HS-DPCCH) feedback information is provided on the uplink carrier to the Node-B and contains information for each downlink carrier.
The Medium Access Control (MAC-ehs) architecture of a WTRU that is capable of implementing DC-HSDPA is shown in FIG. 1. As shown in FIG. 1, the MAC-ehs comprises two (2) HARQ entities. In DC-HSDPA, each cell may be assigned a separate HARQ entity. Accordingly, disassembly and re-ordering are performed jointly for both cells. In addition, a separate HS-DSCH Radio Network Transaction Identifier (H-RNTI) may be given to each.
While not designed to optimize the radio resource, the MAC-ehs architecture for DC-HSDPA, shown in FIG. 1, simplifies the specification and implementation of the WTRU. In accordance with this architecture, the two cells operate almost as two distinct legacy HS-DSCH cells.
To provide power savings options for a WTRU supporting DC-HSDPA, the temporary disabling of the supplementary carrier may be allowed. Such activation and de-activation may be signaled by the Node-B using Layer 1 (L1) messages in the form of HS-SCCH orders. This fast mechanism allows the Node-B to enable, or disable, the supplementary carrier for each WTRU supporting the feature independently.
The introduction of DC-HSDPA however causes a number of issues that need to be resolved to ensure proper and predictable WTRU behavior. In the legacy WTRUs, there may be a single HARQ entity per MAC entity and a single serving HS-DSCH cell. Thus, when the WTRU performs a handover or a channel reconfiguration, it may simply reset the MAC-ehs entirely to start afresh. With DC-HSDPA, however, the MAC-ehs comprises two HARQ entities, which may need to be considered separately in some circumstances. Indeed, when the secondary HS-DSCH serving cell is disabled, resetting the entire MAC-ehs may not be appropriate as the serving HS-DSCH cell may still be using it.
FIG. 2 shows a WTRU procedure for disabling the secondary serving HS-DSCH cell. However, this procedure may not provide all the necessary steps for properly handling the disabling of the second HARQ entity and may be missing the required actions related to the H-RNTI variable.
Additional problems may occur when deactivating a secondary cell in DC_HSPA. When de-activating and re-activating the secondary serving HS-DSCH cell using HS-SCCH orders, it may be desirable to flush the HARQ entity associated with the secondary serving HS-DSCH cell to ensure predictable behavior.
A data indicator (e.g. the “New data indicator”), may be a one bit signal, transmitted as part of the HS-SCCH type 1 to indicate that a Packet Data Unit (PDU) is being transmitted in that HARQ process. This may allow the WTRU to overwrite that part of the HARQ memory. Currently, the network-side HARQ process sets the data indicator in transmitted MAC-hs PDUs. When this is performed, the UTRAN sets the data indicator to the value “0” for the first MAC-hs PDU transmitted by a HARQ process. The data indicator may not be incremented for retransmissions of a MAC-hs PDU. The data indicator may be incremented by one for each transmitted MAC-hs PDU containing new data.
Accordingly, the data indicator may toggle when a new PDU is being transmitted. In the current specifications, it is unclear whether upon re-activation of the secondary HS-DSCH serving cell, via HS-SCCH order, the UTRAN resets the data indicator or not. Thus, in addition to flushing the HARQ entity associated with the secondary serving HS-DSCH cell, it may be desirable to also specify the expected behavior with respect to the data indicator.
Therefore, there exists a need for an improved method and apparatus for handling the activation and deactivation of a supplementary cell.